Completely stock engine with 74,000 miles on it stumbling between idle and 3,500 RPM

[B.Pod]

Hello Pat,
Did you manage to find your problem ?
Could you tell me if your feeling with your car is comparable to this old video ?
[ame="https://www.youtube.com/watch?v=Ddl4nDEzQOM"]https://www.youtube.com/watch?v=Ddl4nDEzQOM[/ame]

[Pat]

Hey B.Pod, thanks for checking in with me. I did not manage to find the problem yet. That said, I haven't experienced the problem since soon after I last posted. I had a friend log it while I was driving, but I could not get the car to stumble as it had previously. I wonder if it has anything to do with the cooler temperatures here now.
Some people here think it is an issue with my coilpack(s). If that were the case, might the problem go away when ambient or intake temperatures are colder?
The video posted above is similar, or maybe the same, type of behavior I have seen in my car. That said, I see it in all gears, not just first. And not just at full throttle.

[OwlDance]

Originally Posted by Pat

Recently my BRZ has begun to stumble at RPMs below about 3,500. The drivetrain is completely stock and never been modified. At first I only noticed it at throttle tip-in. However, over the last few months it has become more frequent, regardless of throttle position. In fact, this morning on the highway in 6th gear at 62 mph I floored it and it seemed to stumble two or three times per second for maybe three or four seconds. I have never seen a single CEL in this car, and the car has always been maintained impeccably well. The spark plugs have 15,000 miles on them. I always use gas from good stations that see a lot of turnover. Primarily that is Shell and Conoco.
Does anyone have any idea what might be causing this? At first it wasn't really a big deal, but it slowly seems to be happening more often in a wider variety of conditions.
Thanks!

Couple things; by stumble at throttle tip in, do you mean that the car feels shuddery when just gently opening onto the throttle? Does it happen when you lift off the throttle as well?

Regarding the bolded text, does it look like this?

[ame]https://www.youtube.com/watch?v=3AU035Pvkp0[/ame]


6th gear at 62mph sounds like really low RPMs on either MT and AT gearing. If I suddenly floor it at low RPMs (sub 2.5k) my car almost "shudders" and the tachometer "jolts" around briefly but only at the initial moment of acceleration, not later on like in the video.

[Pat]

It is not happen just when gently opening the throttle. It can happen at any open throttle position. It never happens when closing the throttle. Only right when I open it some amount.
Yes, my car look like what happens in that video.

[OwlDance]

Check out this thread, then. http://www.ft86club.com/forums/showthread.php?t=66620

Sounds like a DI failure?

[Pat]

Possible. Unlikely.

[Lantanafrs2]

Seems so minor. I wouldn't worry about it. Check all intake hose clamps and clean maf sensor.

[Ultramaroon]

Originally Posted by Pat

I had a friend log it while I was driving, but I could not get the car to stumble as it had previously. I wonder if it has anything to do with the cooler temperatures here now.
Some people here think it is an issue with my coilpack(s). If that were the case, might the problem go away when ambient or intake temperatures are colder?
The video posted above is similar, or maybe the same, type of behavior I have seen in my car. That said, I see it in all gears, not just first. And not just at full throttle.

Pat, post those logs as a baseline. They are valuable.

Do you know how to https://datazap.me/ ?

[Pat]

Thanks, Ultramaroon. I know nothing about logging data. @fika84 did it for me. Maybe he can chime in here.

[Mr_Eyo]

Transient ignition retard is aggressive in the stock ECU and OFT OTS. I think throttle tip in might be able to trigger it despite enrichment, not sure though.

[Ultramaroon]

Originally Posted by Pat

Thanks, Ultramaroon. I know nothing about logging data. @fika84 did it for me. Maybe he can chime in here.

Good friends are cool. Or is it the other way around?


It would be interesting to see if something is operating in a borderline manner. Worth a shot.

[guybo]

A log of fuel trims would be helpful

[22R]

perhaps some bad gas that has gone ???

22R

[Pat]

Originally Posted by 22R

perhaps some bad gas that has gone ???

22R

Possible, but unlikely. It lasted for months through many tankfulls from many different gas stations.